Typically, in automotive air conditioning systems which have an automatic control device, the automatic control device detects the air temperature of an automobile compartment and the ambient air temperature and compares a predetermined or selected air temperature with the detected air temperatures. The ratio of air heated by a heater core with respect to air bypassing the heater core and passing through a duct is determined in accordance with an opening angle of an air mix damper which is controlled by an actuator based on the temperataure comparison. The opening angle of a water valve is also determined in conjunction with that of the air mix damper since the air mix damper is mechanically coupled with the water valve through a wire, mechanical link or the like. The air mix damper is also mechanically coupled with the actuator. In this way, a water valve and air mix damper may be operated together by an actuator.
In the above described automotive air conditioning system, and with reference to FIG. 1, it can be seen that there is hysteresis in the timing of the opening and closing operation of the water valve. Although the water valve is mechanically coupled with the air mixer damper as described above, the water valve does not open until the air mix damper has opened a predetermined amount as defined by a predetermined opening angle. Accordingly, since the air mix damper has already opened to a predetermined opening angle before the water valve opens, the temperature of air initially blown out from an outlet of the air conditioning system is either cool or only slightly heated. In a cold or cool environment, which is typically when heated air is desired, this initial blast of cold or cool air into an already cool automobile produces an uncomfortable feeling for those in the passenger compartment of an automobile.